Grinding wheel



Nv 2, 19371 B. sANFoRb 2,097,803

- GRINDING WHEEL Fiied Feb. 14, y19:55

WIT-Mesem BAAL is @A NFORD Patented Nov. 2, 1937'4 vPATENT OFFICE Norton Company, Worcester, Mass., a corporation of Massachusetts Application February 14, 1935. serial No. 6,441

2 Claims.

This invention relates to grinding wheels and more particularly to a composite grinding wheel for use as a cutting-off wheel whichhas an uter annular grinding portion of diamond grains bonded by an organic bond and an inner central supporting body of a moldable, heat-settable` marily comprises the bulk of the article. These materials of the respective zones or portions of the wheel may be 'combined and shaped into a grinding wheel by suitable means and methods. For example, the wheel may ,be made in accordance with a method which involves hot pressing a mixture of `diamond grains and resinoid bond in a mold in situ with a preformed resinoid core to form a hard, dense mass and heat setting the resinoid.

3-0 It is found, however, that such a method presents certain mechanical diftlculties when apl- `plied to the manufacture of thin cutting-off wheels, which due to the slender dimensions of the article together with the different coeilicients of expansion and unequal shrinkages of' the cured materials in the inner and outer zones of the body and the different maturity characterstics possessed by each of the resinoid compositions used, results in a warped final product. It is accordingly an object of my invention to overcome such dimculties and provide va composite grinding wheel of this type which will not be warped to a detrimental extent after manufacture-and which may be 4economically and easily produced. l

v It is a further object-of my--invention to provide a diamond abrasive wheel of a composite structure havingv a plurality of zones as well as a method of making such an article in which `the shrinkages and coefllcients of expansion thereof may be made substantially equal, and to provide a wheel structure having substantially uniform shrinkage throughout.` l

With these and `further objects in view, as

will be apparent in the following disclosure, my

invention resides in the subject matter described hereinafter and covered by the claims appended hereto.

Referring to the drawing, which illustrates one embodiment of my invention and in which like 5 reference numerals indicatelike parts:

Fig.l l is a plan view of a grinding wheel embodying my invention; and

Fig. 2 is a cross-sectional view, on an enlarged scale, taken on the line 2 2 of Fig. 1. l0

In accordance with my invention, I propose to make a composite grinding wheel of this type having a peripheral annular abrasive body of resinoid bonded diamond grains and an inner zone or central supporting `body `of a resinoid 15 composition integrally united therewith, in which there is incorporated suitable granular inert material in such an amount that the relative shrinkages between the inner vand outer zones are-substantially equalized. That is, the ingredients of 20 the inner and outer zones are so selected and proportioned, and preferably in equal volume percentages in the two zones, that they may be formed into a unitary body of substantially the same structure and shinkage throughout. V 25 Referring Vto the drawing, which shows one 4specific embodiment of my invention, I have there illustrated a' grinding wheel having an outer grinding portion or rim lll nof resinoid bonded diamond granules and a center portion l2 30 of a resinoid composition interspersed with granular inert material. A central holei3 is provided, in the portion l2 for the subsequent mounting of the complete'wheel on a spindle.

'While various resinoid materials may be selected` 35 for bondingthe diamond grains inthe outer rim portion ofthe wheel and for making the center portion thereof and uniting the granular material incorporated therein, I preferably employ a fusible, potentially reactive, heat-settable resin- 40 oidof the phenclictype, such as is commonly known'in the art under the trade-mark Bakelite and obtained as .a condensation product formed by the reaction of phenol andformaldehyde or,Vv by that of their omologues. For the 45 granular inert material in he center portion, I may utilize any mineral or non-mmeral substances which do not change in size materially under the temperature conditions employed during hot pressing'; and, for example, I may em- 60 ploy such granular materials as silicon carbide, crystalline alumina or quartz sand. It is an essential feature -of the invention that the volumel percentages of bond and grains in the two zones ofd the wheel shall be sulclently and 50% by volume of bond, then one should use 50% by volume of bond and 50% by volume of granular ller in the inner zone. identical shrinkages. Reasonable variations in these proportions are, of course, permissible.

As a specific example of a composition which will be suitablefor forming a satisfactory grinding wheel having substantially equal shrinkage throughout, I may utilize the ingredients in the following proportions:

' Outereone Percent by volume Diamond grains (100 mesh grit size) 50 Resinoid bond (phenolic resinoid) 50 Imicr zone Percent by volume Silicon carbide (100 mesh grit size) 50 Resinoid bond (phenolic resinoid) 50 It will, of course, be obvious that different grain sizes of the diamonds and the granular filler may be employed and that the various kinds of resinoids may be used accordingly, as is well known in the art. The density and structure of the product are determined by the nature of the ingradients employed as well as their relative proportions. However, it is preferred to form a wheel structure in which the materials of the two portions are compacted into asubstantially solid, dense mass, that is, one having practically zero porosity.

The materials of the two portions or zones arev mixed separately and in a dry condition until the respective grains of diamond and 1111er have each been thoroughly incorporated with the particular resinoid bond employed therewith which is in a powdered or finely divided condition. The cntral support or inner zone of the wheel is rst formed by 'pressurein a cylindrical mold of the size ydesired for the wheel center which has resulted in a body having compact and reasonably dense structure. Thus, by that method, the dry resinoid mixture as above preparedland incorporating the granular illler is molded by a prelimicentral support. During this operation, care yshould be taken to keep the resinoid ybond from completely reacting so as not to become converted into the infuslble state. 'I'his preformed body I2 is then set into a mold cavity of a size to form the complete wheel and an iron core is inserted into the .center hole i3 to preventdeformation while under the molding pressure. The dry mixture of diamonds and resinoid is then packed into the mold and pressed in place by a suitable hand implement around the outer periphery of the solid center, after which the whole1wheel v mass is then subjected to heatand pressure in naccordance with the usual hot pressing practice which is employed in the art, sc that the various sections are molded together and matured into a hard, integral structure of the desired density. Such procedure as thatv of my prior Patent 1,981,970 may also be used.

It is also feasible to make such a wheel by the following method in which a thin metal ring or annular band is placed in the mold' around and .spaced from the-arbor pin, the diameter and" height of this band being the same as the cor- This insures of the desired grinding properties.

nary compacting operation to produce a strong --ing composition which includes the inert granular material." 'Ihe mixture is then tamped in position. Thereafter, the ring is removed from the mold and the remainder of the mold cavity is then lled with the proper amount of diamond and resinoid mixture to make a rim portion The wheel material is then subjected to heat and pressure whereby the material is molded into an integral unitary body in which the resinoid bond in the two portions is matured and set to its inal iniusible condition.

It will now be appreciated that this invention Y applies toa composite wheel structure in which the central non-abrasive portion shrinks either more or less than does the outer diamond rim portion during cooling of the bond in each of the respective portions after it has been matured by heat. If the composition of the central zone contained materials which served to prevent its contracting as much as does the cured diamond and resinoid mixture in the rim, then the greater rim-,shrinkage would place the center portion under compression and cause warpage or buckling of this center portion. Similarly, if the center portion should shrink more than the outer rim, then either the rim would be placed under radial tension to produce warping ofthe center, orthe two zones might even separate due to the.

two zones. That is, each bond should occupy the same percentage per unit of volume in each of the zones. For convenience of manufacture, it is also desirable to have the grain size of the diamonds and that of the granular filler in the respective zones of substantially the same size. It is`important, however, if strength is to be considered. that the grains of granular inert material in the inner zone be made of a fine grit size, whether or not the diamond grains employed in the rim portion are small in size. Nevertheless, there must be the ysame total volume of solids per unit of volume in each of the zones. Also, if the resinoids differ in their shrinkage coefiicients, then due allowance will be made for this in determiningf the volume percentages thereof. Hence, the main object of this invention is satisfied by so selecting and proportioning the ingredients that the coelcients of shrinkage of the two zones in the completed articlare substantiallylalike. v Y' Having thus described my invention, what I claim as new and desire to secure by Letters Patent is: -1 Vl. Agthinucuttingoif grinding wheel comprising outer annular abrasive zone of diamond grains and a reacted resinoid bond compacted and proportioned to provide al dense body and a central supporting zone of a granular filler other than diamond and reacted resinoid'bond compacted `into a rigid support for the outer zone,

said l:granular filler and its bond Ain the inner zone being so proportioned that lthe bond occuples substantially the same volume percentage as does the bond of the abrasive zone.

2. A thin cutting ofi grinding wheel compris- 5 ing an outer annular abrasive zone of diamond p grains and a reacted resinoid bond compacted Xand proportioned to provide a dense body and a central supporting zone of silicon carbide grains 

